JPH0533685A - Engine - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] The air-fuel ratio is lower than the theoretical air-fuel ratio in the low load range.
On the other hand, in the high load range, the cylinder temperature in the high load range is lowered on the premise of an engine that gradually increases the fuel mixture ratio according to the load and obtains output according to the load. Improve thermal efficiency. [Configuration] The engine 1 has a sub chamber 20, and the sub chamber 20 is
The sub-chamber port 20a opened and closed by the sub-chamber valve 21 is opened to the combustion chamber 4, and the sub-chamber valve 21 is opened and closed at a predetermined timing in synchronization with the output shaft of the engine in the high load region, and the low load region. Then it is closed. The air-fuel mixture trapped in the sub-chamber 20 is cooled in the sub-chamber 20, the cooled air-fuel mixture is replaced with the air-fuel mixture in the combustion chamber 4, and the temperature of the air-fuel mixture in the combustion chamber 4 decreases. To do. Therefore, in the high load range where the fuel mixture ratio is increased according to the load,
Due to the action of the sub chamber 20, the temperature inside the cylinder is lowered, which improves the thermal efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine, that is, an internal combustion engine, and more particularly to an engine for improving the thermal efficiency of the engine.

[0002]

2. Description of the Related Art Recently, engines have been used as fuel supply means.
In many cases, a fuel injection valve is mounted and the fuel injection valve is controlled by an electronic control unit (see Japanese Patent Publication No. 2-36772). In this type of engine, there is an advantage that the air-fuel ratio of the air-fuel mixture (fuel mixture ratio with respect to intake air) can be freely controlled. Here, the Japanese Patent Publication No. 2-36772 discloses a so-called lean burn engine in which the engine is operated under an air-fuel ratio set leaner than the stoichiometric air-fuel ratio. ..

By the way, in the engine, it is more efficient to make the air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel ratio. This point will be described in detail below.

In an engine, that is, an internal combustion engine, mechanical work is taken out by utilizing the pressure increase (increase ΔP in cylinder pressure) due to combustion of fuel supplied to a combustion chamber. Therefore, the cylinder pressure rise ΔP due to combustion
The larger the value, the better the job. Here, the increase ΔP of the in-cylinder pressure is represented by the following equation, assuming equal volume combustion.

ΔP = (εR / V) × (Q / C _v ) ... (1)

Where ε: compression ratio R: gas constant Q: calorific value of fuel V: combustion chamber volume C _v : constant volume specific heat

Next, the temperature change of the rise in cylinder pressure ΔP will be examined. Differentiating the above equation (1) gives the following equation (2).

D (ΔP) / dT = − (εR / V) X (Q / C _v ² ) X (dC _v / dT) (2)

By the way, it is known that the constant volume specific heat C _v increases as the temperature rises (see FIG. 1). Therefore, (dC _v / dT)> 0, and the right side of the above equation (2) has a negative value.

That is, d (ΔP) / dT <0, and the higher the cylinder temperature T, the smaller the cylinder pressure increase ΔP.
In other words, the lower the cylinder temperature T, the higher the cylinder pressure ΔP.
Will grow up and work better.

Next, considering the relationship between the air-fuel ratio of the air-fuel mixture and the temperature rise (cylinder temperature T) accompanying combustion, if the air-fuel ratio is leaner than the theoretical air-fuel ratio (lean bar). In the case of an internal combustion engine), a portion of the amount of heat generated by combustion is absorbed by the surplus air, so the in-cylinder temperature T becomes low. Of course,
As the lean degree of the air-fuel ratio increases, the amount of surplus air increases, so the in-cylinder temperature T decreases.

As is clear from the above examination, when the lean burn engine, that is, when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the cylinder temperature T becomes lower, which causes the cylinder pressure to rise. As ΔP increases, we will work well. Further, the leaner the air-fuel ratio is, the better the work is done (the thermal efficiency is further improved).

Further, in reality, if the in-cylinder temperature T decreases, the heat transfer to the wall surface of the combustion chamber also decreases, and the cooling loss can be reduced. Therefore, also in terms of this cooling loss, the leaner the air-fuel ratio, the higher the thermal efficiency.

Next, the conventional air-fuel ratio setting in the lean burn engine will be described. Figure 6 shows natural aspiration (N
This is a representation of an A) type engine. As shown in FIG. 6, in the low load region and the medium load region (these regions are hereinafter referred to as the low load region in comparison with the high load region, which will be described later), mixing such as A / F = 18 is performed. The air-fuel ratio of the air is controlled to be a predetermined lean air-fuel ratio,
In the high load region, it is customary to gradually increase the fuel mixture ratio (gradually increase the air-fuel ratio) to secure an output according to the load. The same applies to the engine with the supercharger.

As described above, even in the lean burn engine, the reason why the air-fuel ratio is made rich according to the load in the high load region is that the capacity of the intake system is limited, so that Since the output cannot be sufficiently output as it is, the output according to the load can be obtained by increasing only the fuel supply amount, and the in-cylinder temperature can be reduced by making the air-fuel ratio rich.

[0016]

However, making the air-fuel ratio rich in the high load region is nothing but reducing the thermal efficiency in this region. In other words, in the low load region, even though the thermal efficiency is increased under the lean air-fuel ratio, if the thermal efficiency is reduced in the high load region, the effect of improving the overall thermal efficiency of the engine is small. Will be.

Therefore, on the premise that the air-fuel ratio is gradually made rich in a high load region to secure an output according to the load, the object of the present invention is to lower the in-cylinder temperature in this region to enhance the thermal efficiency. The purpose is to provide the engine.

[0018]

In order to achieve the above technical object, in the present invention, the air-fuel ratio of the air-fuel mixture supplied to the engine is made leaner than the theoretical air-fuel ratio in the low load region. On the other hand, in the high load region, on the other hand, in the high load range, the engine is designed to secure the output according to the load by increasing the fuel mixture ratio as the load increases,

A sub-chamber formed in the main body of the engine and opening to the combustion chamber and a sub-chamber valve for opening and closing the opening of the sub-chamber are provided, and the sub-chamber valve compresses at least in the high load region. The valve is opened in the middle of the stroke and closed during the end of the compression stroke or the beginning of the explosion stroke.

[0020]

With the above construction, in the high load range, the hot air-fuel mixture due to compression is enclosed in the sub chamber and cooled in the sub chamber. Then, the air-fuel mixture cooled in the sub chamber is replaced with a part of the air-fuel mixture in the combustion chamber in the next compression stroke, and as a result, the air-fuel mixture in the combustion chamber is cooled (the temperature inside the cylinder decreases). Therefore, the higher the temperature of the air-fuel mixture introduced into the sub-chamber, the greater the cooling effect in the sub-chamber, which makes it possible to greatly reduce the in-cylinder temperature.

As described above, the lower the in-cylinder temperature, the better the work. This point will be described below from another viewpoint.

Now, the calorific value Q of the fuel is expressed by the following equation. Q = Cv ・ G ・ △ T ・ ・ ・ (3)

Where Cv: constant volume specific heat G: mass of air-fuel mixture introduced into the combustion chamber ΔT: temperature rise due to combustion (increase in cylinder temperature)

When the above equation (3) is modified, the following equation (4) is obtained. ΔT = Q / Cv · G (4) As can be understood from the equation (4), when Q and G are constant, the smaller Cv is, the larger ΔT is.

By the way, as described above, the constant volume specific heat Cv
Increases as the temperature T increases (see FIG. 1).
In other words, the smaller the in-cylinder temperature T, the smaller the constant volume specific heat Cv. Therefore, the smaller the in-cylinder temperature T is, the larger the increase ΔT in the in-cylinder temperature due to combustion is.

Here, the larger the temperature rise ΔT in the cylinder is,
Since the cylinder pressure greatly increases (ΔP is large),
The smaller the in-cylinder temperature T, the greater the increase in the in-cylinder pressure ΔP. In other words, put the same amount of fuel,
When the obtained calorific values are the same, the smaller the in-cylinder temperature T is, the larger the in-cylinder pressure increase ΔP is, and therefore the better the work is performed (the better the thermal efficiency is).

Regarding the sub chamber valve, when considering the closing timing of the sub chamber valve, if the temperature rise due to compression of the air-fuel mixture in the combustion chamber is to be utilized to the maximum,
The closing timing of the sub chamber valve may be set to the compression top dead center. Alternatively, if the pressure increase due to combustion is also used to the maximum extent, it is better to close the sub chamber valve as late as possible (the crank angle that reaches the maximum combustion pressure is after compression top dead center (ATD
C) About 30 deg).

Here, the actual combustion state varies greatly with each cycle, as shown in the acupressure diagram of FIG.
Therefore, if the sub chamber valve was opened until the deviation (variation) of the in-cylinder pressure was large, the pressure, density, and temperature of the air-fuel mixture trapped in the sub chamber would fluctuate in each cycle. Not preferable.

Considering FIG. 2 from this point of view, in the example of engine specifications and operating conditions shown in FIG. 2, the pressure fluctuation in the combustion chamber occurs about 20 deg after the ignition timing.
It is after a while. Therefore, if the sub-chamber valve is closed immediately before the deviation (variation) of the pressure increase due to combustion occurs, it is possible to suppress the influence of combustion fluctuation and enhance the cooling effect of the air-fuel mixture. On the other hand, if the influence of the pressure fluctuation due to the combustion is to be avoided, the sub chamber valve may be closed near the ignition timing. That is, the sub chamber valve may be closed at the end of the compression stroke.

Specifically, the opening timing of the sub chamber valve may be determined in relation to the closing timing of the sub chamber valve. That is, even if the sub-chamber valve is opened, the air-fuel mixture in the sub-chamber cannot be immediately replaced with the air-fuel mixture in the combustion chamber. This replacement requires some time. However, when the sub chamber valve is opened too early, the compression stroke is performed under the volume of the combustion chamber plus the volume of the sub chamber, resulting in a large compression loss.

Therefore, the opening timing of the sub-chamber valve may be set as late as possible after the compression stroke (after closing the intake valve) and at the timing that can secure the time required to replace the air-fuel mixture in the sub-chamber. The opening timing of this sub-chamber valve is in the middle of the compression stroke. Of course, the opening timing of the sub chamber valve may be finally determined by an experiment.

As a conventional technique structurally similar to the present invention, Japanese Patent Laid-Open Nos. 54-116512 and 54-9 are available.
There is an engine with a sub chamber disclosed in Japanese Patent No. 80408.
This engine with a sub-chamber includes a sub-chamber that opens to the combustion chamber and a sub-chamber valve that opens and closes the opening of the sub-chamber, and this point is common to the present invention.

However, in this engine with a sub-chamber, the sub-chamber valve is opened at the closing timing of the intake valve and the mixture in the sub-chamber is utilized (e.g. The present invention differs from the present invention in that a strong swirl is generated in the combustion chamber (using the differential pressure).

[0034]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Reference numeral 1 shown in FIG. 3 is an engine, and the engine 1 has a combustion chamber 4 defined by a piston 3 inserted into a cylinder bore 2, and an ignition plug 5 is disposed so as to face the combustion chamber 4. ing.

An intake port 6 and an exhaust port 7 are opened in the combustion chamber 4, and an intake valve 8 is provided in the intake port 6.
The exhaust port 7 is provided with an exhaust valve 9, and the intake valve 8 and the exhaust valve 9 are opened and closed at a predetermined timing in synchronization with an engine output shaft (not shown). It

In the intake passage 10 connected to the intake port 6, the air cleaner 1 is provided in order from the upstream side to the downstream side.
1, an air flow meter 12 for detecting the intake air amount, a throttle valve 13 are provided, and a fuel injection valve 14 is provided so as to face the intake port 6. That is, the engine 1 is a conventionally known Otto-cycle gasoline 4-cycle engine.

In FIG. 3, reference numeral 15 is a control unit, and this control unit 15 is composed of, for example, a micro computer, and as is known, CP
U, ROM, RAM, etc. are provided. Signals from the sensors 12, 16 and 17 are input to the control unit 15. The sensor 12 detects the intake air amount as described above. The sensor 16 detects the opening of the throttle valve 13, that is, the load. The sensor 17 detects the engine speed.
Then, a control signal is output from the control unit 15 to the spark plug 5 and the fuel injection valve 14.

Since the control of the ignition plug 5 performed by the control unit 15, that is, the control of the ignition timing is the same as the conventional one, the description thereof will be omitted. On the other hand, the control of the fuel injection valve 14 performed by the control unit 15, that is, of the injection timing control and the injection amount control, the injection timing control is the same as the conventional one. The control, that is, the air-fuel ratio control of the air-fuel mixture is as shown in FIG.

Referring to FIG. 4, the line A represents the lean potential of the engine 1.
That is, as the load increases, the amount of fuel supplied into the combustion chamber 4 increases, so the lean limit of the air-fuel ratio becomes
The larger the load, the larger the load (the larger the load, the more leaning is possible). Therefore,
In the air-fuel ratio control here, a target air-fuel ratio leaned to the lean potential A corresponding to the load is set in a region where the intake amount can be increased (low load region).

On the other hand, in a region where the amount of intake cannot be increased according to the load, that is, in a high load region where the capacity of the intake system is exceeded as shown by line B in FIG. 4, the fuel supply amount is increased according to the load. By doing so, the output according to the load is secured. Therefore, in this high load range, the target air-fuel ratio is made richer as the load increases. The relationship between the target air-fuel ratio and the load is shown by line C in FIG.

Returning to FIG. 3, the engine 1 includes the sub chamber 20.
have. The sub chamber 20 has a sub chamber port 20a opened to the combustion chamber 4, and a sub chamber valve 21 is provided in the sub chamber port 20a.
The sub-chamber valve 20a is opened and closed by the sub-chamber valve 21 in the high load region, and the sub-chamber port 20a is closed by the sub-chamber valve 21 in the low load region. ..

FIG. 5 shows an example of opening / closing timing of the sub chamber valve 21 in the high load range. As is apparent from FIG. 5, the closing timing of the sub chamber valve 21 is set to ABDC 160 deg, which is the same as the ignition timing, and the sub chamber valve 21 is opened about 70 deg before this closing timing. The closing timing of the intake valve 8 is about 50 deg after the top dead center has passed.

With the above-mentioned structure, a part of the air-fuel mixture in the combustion chamber 4 is closed in the sub-chamber 20 by the sub-chamber valve 21 which is opened and closed in the compression stroke, cooled in the sub-chamber 20, and the next mixture is cooled. In the compression stroke, the air-fuel mixture cooled in the sub chamber 20 is replaced with a part of the air-fuel mixture in the combustion chamber 4.

As a result, in the high load region, the combustion chamber 4
The temperature of the air-fuel mixture inside (in-cylinder temperature) is lower than that of a normal engine that does not have the sub chamber 20, and the thermal efficiency of the engine 1 in the high load range is improved.

Further, the fact that the in-cylinder temperature decreases in the high load region is also advantageous as a countermeasure against knocking, and the compression ratio of the engine 1 can be set to a high compression ratio.

Explaining the relationship between the lean burn and the high compression ratio, when the compression ratio of the engine 1 is increased, the cylinder volume becomes smaller at every crank angle than that of the low compression ratio engine. If the supply amount is the same, the fuel molecule density in the combustion chamber 4 increases and the ignitability and combustibility are improved. Therefore, if the air-fuel ratio is the same, the thermal efficiency is improved only by increasing the compression ratio, but further leaning is possible.

From the above, in the high load range, in addition to the improvement of the thermal efficiency due to the decrease of the in-cylinder temperature by the sub chamber 20, the higher compression ratio results in the higher heat efficiency and the leaner range in the low load range. It is possible to improve the thermal efficiency by increasing the temperature.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and includes the following modifications.

(1) Conventional air-fuel ratio control, that is, as shown in FIG. 6, the target air-fuel ratio is set to a predetermined lean air-fuel ratio in the low load range, while the target air-fuel ratio is set in the high load range according to the load. When enriching the fuel ratio, the sub-chamber 20 may be used in the high load range to lower the in-cylinder temperature.

(2) In the above embodiment, the target air-fuel ratio in the low load range may be set stepwise according to the lean limit.

(3) In the above-mentioned embodiment and the modified example, the sub-chamber 20 is used in the high load range. However, in the low load range, the sub-chamber is disclosed in Japanese Patent Laid-Open No. 54-116512. 20 may be used to generate a strong swirl in the combustion chamber 4. In this case, the sub chamber valve 2
The opening / closing timing of 1 is variable, and the intake valve 8
It is preferable to open the sub chamber valve 21 immediately after closing the valve.

(4) The present invention can be applied to the engine 1 equipped with a supercharger. That is, in the case of an engine with a supercharger, the in-cylinder temperature may be lowered by using the sub chamber 20 in a high load range exceeding the supercharging capacity of the supercharger. According to this modified example, it is also effective as a knocking countermeasure for an engine having an extremely large boost pressure.

[0053]

As is apparent from the above description, according to the present invention, the thermal efficiency is improved by the lean air-fuel ratio in the low load region, and the in-cylinder temperature is lowered in the high load region by utilizing the sub chamber. By improving the thermal efficiency due to, it is possible to improve the thermal efficiency in the entire region. In addition, since the knocking problem in the high load region is reduced by the decrease in the in-cylinder temperature, the compression ratio of the engine can be increased, and the thermal efficiency can be improved in terms of this compression ratio.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between specific heat (constant volume specific heat) of mixture and temperature.

FIG. 2 is a typical acupressure diagram of an engine.

FIG. 3 is a schematic diagram of an engine according to an embodiment.

FIG. 4 is a diagram showing the content of air-fuel ratio control of the engine according to the embodiment.

FIG. 5 is a view showing an example of opening / closing timing of a sub chamber valve.

FIG. 6 is a diagram showing a conventional example of engine air-fuel ratio control.

[Explanation of symbols]

 1 Engine 3 Piston 4 Combustion Chamber 5 Spark Plug 8 Intake Valve 12 Air Flow Meter 14 Fuel Injection Valve 15 Control Unit 16 Throttle Opening Sensor 20 Sub Chamber 20a Sub Chamber Port 21 Sub Chamber Valve Opening to Combustion Chamber

Claims (1)

Claims: 1. The air-fuel ratio of the air-fuel mixture supplied to the engine is set leaner than the stoichiometric air-fuel ratio in the low load region, while the load becomes large in the high load region. In the engine, the output corresponding to the load is secured by increasing the fuel mixing ratio, and a sub-chamber formed in the main body of the engine and opening to the combustion chamber and an opening of the sub-chamber are provided. And a sub-chamber valve that opens and closes, wherein the sub-chamber valve is at least in the high load region,
An engine that is opened in the middle of the compression stroke and closed during the end of the compression stroke or the beginning of the explosion stroke.